5,692 research outputs found
The determination of urea in seawater
A clinical method for the determination of urea in blood and urine (Beale and Croft 1961) has been modified for the determination of smaller quantities of urea (1-20 µg N/l) in seawater
Statistical Description of Acoustic Turbulence
We develop expressions for the nonlinear wave damping and frequency
correction of a field of random, spatially homogeneous, acoustic waves. The
implications for the nature of the equilibrium spectral energy distribution are
discussedComment: PRE, Submitted. REVTeX, 16 pages, 3 figures (not included) PS Source
of the paper with figures avalable at
http://lvov.weizmann.ac.il/onlinelist.htm
First measurements of the flux integral with the NIST-4 watt balance
In early 2014, construction of a new watt balance, named NIST-4, has started
at the National Institute of Standards and Technology (NIST). In a watt
balance, the gravitational force of an unknown mass is compensated by an
electromagnetic force produced by a coil in a magnet system. The
electromagnetic force depends on the current in the coil and the magnetic flux
integral. Most watt balances feature an additional calibration mode, referred
to as velocity mode, which allows one to measure the magnetic flux integral to
high precision. In this article we describe first measurements of the flux
integral in the new watt balance. We introduce measurement and data analysis
techniques to assess the quality of the measurements and the adverse effects of
vibrations on the instrument.Comment: 7 pages, 8 figures, accepted for publication in IEEE Trans. Instrum.
Meas. This Journal can be found online at
http://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=1
Defect Dynamics for Spiral Chaos in Rayleigh-Benard Convection
A theory of the novel spiral chaos state recently observed in Rayleigh-Benard
convection is proposed in terms of the importance of invasive defects i.e
defects that through their intrinsic dynamics expand to take over the system.
The motion of the spiral defects is shown to be dominated by wave vector
frustration, rather than a rotational motion driven by a vertical vorticity
field. This leads to a continuum of spiral frequencies, and a spiral may rotate
in either sense depending on the wave vector of its local environment. Results
of extensive numerical work on equations modelling the convection system
provide some confirmation of these ideas.Comment: Revtex (15 pages) with 4 encoded Postscript figures appende
Cellular automata approach to three-phase traffic theory
The cellular automata (CA) approach to traffic modeling is extended to allow
for spatially homogeneous steady state solutions that cover a two dimensional
region in the flow-density plane. Hence these models fulfill a basic postulate
of a three-phase traffic theory proposed by Kerner. This is achieved by a
synchronization distance, within which a vehicle always tries to adjust its
speed to the one of the vehicle in front. In the CA models presented, the
modelling of the free and safe speeds, the slow-to-start rules as well as some
contributions to noise are based on the ideas of the Nagel-Schreckenberg type
modelling. It is shown that the proposed CA models can be very transparent and
still reproduce the two main types of congested patterns (the general pattern
and the synchronized flow pattern) as well as their dependence on the flows
near an on-ramp, in qualitative agreement with the recently developed continuum
version of the three-phase traffic theory [B. S. Kerner and S. L. Klenov. 2002.
J. Phys. A: Math. Gen. 35, L31]. These features are qualitatively different
than in previously considered CA traffic models. The probability of the
breakdown phenomenon (i.e., of the phase transition from free flow to
synchronized flow) as function of the flow rate to the on-ramp and of the flow
rate on the road upstream of the on-ramp is investigated. The capacity drops at
the on-ramp which occur due to the formation of different congested patterns
are calculated.Comment: 55 pages, 24 figure
Toda Lattice Solutions of Differential-Difference Equations for Dissipative Systems
In a certain class of differential-difference equations for dissipative
systems, we show that hyperbolic tangent model is the only the nonlinear system
of equations which can admit some particular solutions of the Toda lattice. We
give one parameter family of exact solutions, which include as special cases
the Toda lattice solutions as well as the Whitham's solutions in the Newell's
model. Our solutions can be used to describe temporal-spatial density patterns
observed in the optimal velocity model for traffic flow.Comment: Latex, 13 pages, 1 figur
Kinetic equation for a dense soliton gas
We propose a general method to derive kinetic equations for dense soliton
gases in physical systems described by integrable nonlinear wave equations. The
kinetic equation describes evolution of the spectral distribution function of
solitons due to soliton-soliton collisions. Owing to complete integrability of
the soliton equations, only pairwise soliton interactions contribute to the
solution and the evolution reduces to a transport of the eigenvalues of the
associated spectral problem with the corresponding soliton velocities modified
by the collisions. The proposed general procedure of the derivation of the
kinetic equation is illustrated by the examples of the Korteweg -- de Vries
(KdV) and nonlinear Schr\"odinger (NLS) equations. As a simple physical example
we construct an explicit solution for the case of interaction of two cold NLS
soliton gases.Comment: 4 pages, 1 figure, final version published in Phys. Rev. Let
Localised and nonlocalised structures in nonlinear lattices with fermions
We discuss the quasiclassical approximation for the equations of motions of a
nonlinear chain of phonons and electrons having phonon mediated hopping.
Describing the phonons and electrons as even and odd grassmannian functions and
using the continuum limit we show that the equations of motions lead to a
Zakharov-like system for bosonic and fermionic fields. Localised and
nonlocalised solutions are discussed using the Hirota bilinear formalism.
Nonlocalised solutions turn out to appear naturally for any choice of wave
parameters. The bosonic localised solution has a fermionic dressing while the
fermionic one is an oscillatory localised field. They appear only if some
constraints on the dispersion are imposed. In this case the density of fermions
is a strongly localised travelling wave. Also it is shown that in the multiple
scales approach the emergent equation is linear. Only for the resonant case we
get a nonlinear fermionic Yajima-Oikawa system. Physical implications are
discussed.Comment: 7 pages, LaTeX, no figures. to appear in Europhysics Latter
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